The Census is expensive, difficult and controversial. But we do it because our numbers matter

I still bear the mental scars of a question on a philosophy exam in college that left me whimpering at its wicked simplicity: "Could the number two change its properties?" I'd been raised to think numbers were as close to reliable as anything could be, so clean and clear and immune to argument. Some are odd, some round, some lucky, but three will always be one less than four.

This is the season when we are reminded that you can safely and reliably count just about anything other than people. Census comes from the Latin censere, which, tellingly, does not mean...